Breast biopsy under conscious
following case will emphasize conscious sedation and its potential
general pre-operative evaluation
respiratory depression: detection, management
laryngeal mask airway
reversal of sedation.
patient, a 40-year-old and otherwise healthy woman, comes for breast biopsy.
procedure is usually performed in two stages: first a radiologist places a
nee-dle percutaneously into the lump. Next, the patient reports to the
operating room for removal of the lump, pathologic confirmation of the margins,
and perhaps a larger procedure depending on the circumstances.
She has no chronic medical problems but recently detected a lump in her right
breast. Needle localization was performed in radiology this morning and she now
presents to the operating suite for lumpectomy.
healthy patient requires very little additional anesthetic work-up. We ask
about the following:
(i) a brief review of systems, including
gastro-esophageal reflux disease (negative)
(ii) past surgical procedures (none)
(iii) family history of anesthetic problems (none)
(iv) current medications, including over-the-counter
herbal remedies (none)
(v) allergies, including latex (none)
(vi) habits including smoking, alcohol and drugs (none)
physical examination, including airway:
white woman in no acute distress; weight 60 kg; height 5 4 (165 cm) BP120/80
mmHg; HR 80 beats/min; respiratory rate 12 breaths/min
Mallampati I, 4 fingerbreadth(fb) mouth opening, 4 fb thyromental distance,
S2 no murmur
Lungs clear to auscultation
with needle in right breast.
pre-operative laboratories and studies (none are indicated) This healthy patient would be classified as
preparation: We discuss the risks/benefits of the various anesthetic options.
She selects i.v. sedation and we administer an anxiolytic (midazolam (Versed®)
2 mg i.v.).
surgeon will inject a local anesthetic, blunting the majority of the pain from
the procedure, while the anesthesiologist is present to observe and reassure
the patient, administer additional anxiolytics or opioids, and treat any
hemodynamic instability. Most patients prefer not to be awake and aware during
such a pro-cedure. Anesthetic options include (i) conscious sedation, in which
the patient remains arousable and in control of her own airway, but free from
anxiety and generally unaware of the procedure, and (ii) general anesthesia in
which the air-way must be managed by mask, laryngeal mask airway or
endotracheal tube. After we explain the risks to the patient, she selects i.v.
of sedation: Once in the operating room, we apply standard monitors
(non-invasive blood pressure, ECG, pulse oximetry), taking care to avoid the
right arm for blood pressure cuff application in case axillary node dissection
becomes necessary. Following a 50 mg bolus of propofol, we start an infusion at
50–80 mcg/kg/min. The patient’s saturation declines to 95% so oxygen via nasal
cannula is applied at 4L/min and the saturation rapidly returns to 100%.
to obtain a therapeutic blood level rapidly, we give an initial bolus of
propofol and follow it with a continuous infusion to maintain the level of
seda-tion. When the patient is sufficiently drowsy, positioning, prepping and
draping can commence. While it should not be necessary, everyone in the room
must be reminded the patient is “awake.” This includes a sign on the door for
those entering later. Unfortunately, the decorum of the OR is not routinely
suitable for the awake patient. As in any workplace, discussions may depart
from the task at hand, causing concern for a patient who is aware, and might
recall irrelevant or objectionable talk.
of anesthesia: We titrate the propofol infusion to the desired effect with a
goal of arousability with slurred speech, but respiratory and hemodynamic
injection of local anesthetic into the breast, she complains of pain. We
administer fentanyl 50 mcg, and increase the propofol infusion rate. One minute
later the patient moans and we respond with another 50 mcg fentanyl. Fifteen
minutes later the SpO2 is falling rapidly. On examination we
discover she is apneic. We start ventilation by mask, but encounter difficulty
maintaining an open upper airway. When things do not get much better after
placing an oral airway, we insert a laryngeal mask airway (LMA) and achieve
good air movement. Her saturation rebounds rapidly.
than 2 mcg/kg fentanyl should not cause apnea. Alone, that is usually true,
however opioids combined with sedatives act synergistically to depress
ventila-tion. Had we been monitoring respiratory pattern/rate we would have
noticed that her breathing became dangerously slow a couple of minutes after we
had given fentanyl. Our detection method (pulse oximetry here) failed us
because we gave so much supplemental oxygen that her PaO2 was
probably close to 200 mmHg as long as she was breathing, if slowly. Thus she
had to be almost apneic for her PaO2 to fall below 80 mmHg, where a
drop in the SpO2 would be expected.
case a smaller dose of fentanyl might have been more appropriate, or perhaps
the use of a shorter acting opioid such as remifentanil. More importantly, we
should monitor respiratory rate, either via a precordial stethoscope
(imprac-tical for this particular surgical procedure) or by a capnograph
attached through the nasal cannula. At the first sign of oversedation, we could
have breathed for her and administered a reversal agent (naloxone). However the
side effects of reversal must also be considered, particularly in the middle of
managing the apnea, several issues need be recognized. If the problem is
central, e.g., oversedation impairing respiratory drive, the patient’s lungs
will have to be manually ventilated. If soft tissue obstruction of the upper
airway is to blame, we need to establish an open airway with the help of an
oral airway or LMA. In this difficult phase of being neither awake nor
completely anesthetized, manipulation of the upper airway can lead to
laryngospasm, coughing, vomiting, and significant movement (usually much to the
dismay of the surgeon). In our case the problem was central depression and the
patient tolerated the LMA. At this point we usually add nitrous oxide and
increase the propofol infusion rate so she will continue to tolerate the
device. This increased sedation is limited by the need to have her resume
from anesthesia: During closure of the incision, we titrate down the propofol
and eventually discontinue the nitrous oxide. When the bandage has been
applied, and the patient is awake and breathing with a good respiratory
pattern, we suction the posterior pharynx and remove the LMA.
care. There should be little pain from this procedure. We turn the care of the
patient over to the postanesthesia care unit (PACU) nurses with standing orders
of morphine for pain, and an anti-emetic, as needed.
advantage of the LMA is that, if the patient is breathing spontaneously but not
fully awake, she can be transported to the PACU with the LMA in place, where
the nurse removes it at the appropriate time.
When the patient is fully awake and tolerating oral intake, she can be
dis-charged home with a caregiver, prescription for an analgesic and instructions
not to drive for 24 hours.